Since neutral is a safety and return path it never disconnects thatís how you die. Line voltage is always the disconnect on all AC apps household wiring etc which is why itís easy to trace back. Op stats are on the blower house along with the thermal fuse physically adjacent. Thermal fuses and tcoís are single blow components for safety but they can blow by age too. Hi limit is on burner shroud which acts as op stat till temp gets hot enough at primary op stat to take Over to protect over heating of thermal fuse under normal ops. Hi limit and op stat are discs. Under failure thermal fuses blow when heat doesnít shut off and you have good airflow. Tco are opposite and blow from lack of air flow and over heating at burner/element. What you should hear is first coil click, ignitor glow, click then fire, ignitor off until reaches temp then click fire off, cool down, click, then starts over.